It is essential for normal breathing that the space within the pleural cavity surrounding the lungs be free of liquid and be subject to a negative pressure so as to draw the lungs outwardly to fill this pleural cavity in order to permit proper breathing. Any invasion of the pleural cavity such as caused by lung surgery or foreign objects which pierce the rib cage or such as occur, for example, where the patient has pleurisy, generates fluids in the pleural cavity which tend to obstruct normal breathing. It is necessary to provide a device which can remove these fluids from the pleural cavity and at the same time ensure that the desired degree of negative pressure is maintained within the pleural cavity.
One of the basic types of apparatus which have been used for this purpose is shown, for example, in U.S. Pat. Nos. 3,363,626 and 3,363,627, which are herein incorporated by reference. This apparatus is known as an underwater drainage apparatus and provides three chambers, one chamber comprising a collection chamber for collecting the fluids drained from the pleural cavity through a thoracotomy tube, a second chamber known as an underwater seal chamber which protects the pleural cavity from being subject to atmospheric pressure, and a third chamber known as a pressure manometer chamber which serves to regulate the degree of negative pressure within the pleural cavity. This type of apparatus has been highly successful in both removing fluids from the pleural cavity and in maintaining the desired degree of negativity within the pleural cavity. However, such an apparatus required prefilling the underwater seal chamber with water and also prefilling the pressure manometer chamber to the desired level to maintain the desired degree of negativity within the pleural cavity.
In order to avoid the necessity and problems of having to prefill chambers in a drainage device, the underwater seal chamber is located at the lower end of the thorocotomy tube. In this manner, the underwater seal is formed by liquid drained from the patient's pleural cavity. Drainage systems of this nature and disclosed in U.S. Pat. No. 4,105,603 and application Ser. Nos. 107,329 and 120,295, which are herein incorporated by reference.
It has been found that doctors frequently will "milk" the thoracotomy tubes in an effort to remove any clots or obstructions from the tube. This milking of the tube is achieved by squeezing the flexible thoracotomy tube adjacent the upper end and drawing the fingers down the tube to cause the fluids within the tube to be passed out the lower end of the tube. Obviously, this action has the effect of substantially lowering the degree of negativity within the pleural cavity. Such high negativity can be damaging to the pleural cavity and may also cause the liquid within the underwater seal chamber to be drawn up into the pleural cavity. In addition, even with a surgical drainage device having a separate underwater seal chamber, the entire seal can be lost during periods of high negativity in the pleural cavity. The loss of the water seal has the potential for serious damage in the event that the suction becomes discionnected. Thus, there is need for a means for providing instant relief for the condition of excess negativity in the pleural cavity.
In applicant's pending U.S. application Ser. No. 256,152, a metered air pump is disclosed by which excess negative pressure can be relieved by pumping as many small units of air into the thoracotomy tube as necessary. However, relief is only provided upon actuation of the device by an attendant or the like and thus does not operate automatically.